Simple event manager in python

event_manager.py

class Mom:    
    def on_door_opened(self):
        print("Who's there?")
        
        
class Priest:
    def on_door_opened(self):
        print("Is it police? Run!")


class EventManager:
    def __init__(self):
        self._handlers = {}
    
    def add_handler(self, event_name, handler):
        if event_name not in self._handlers:
            self._handlers[event_name] = []
            # event_name is not yet used, so prepare an empty bag
            
        self._handlers[event_name].append(handler)
        
    def emit(self, event_name):
        for handler in self._handlers[event_name]:
            handler()
            
           
        
manager = EventManager()


mom = Mom()
priest = Priest()

manager.add_handler("DOOR_OPENED", mom.on_door_opened)
manager.add_handler("DOOR_OPENED", priest.on_door_opened)

manager.emit("DOOR_OPENED")